The invention relates to a method for rotating rolls. The invention also relates to a device for rotating rolls. Furthermore, the invention relates to an arrangement for a rotating device.
As is well known, for wrapping of cylindrical pieces, such as paper rolls, wrapping devices known as such are used, which devices perform the wrapping by means of a wrapping film, typically a transparent stretch film or a thin plastic film. One known wrapping device is disclosed in the patent publication U.S. Pat. No. 5,086,610. The wrap is guided around the mantle of the piece and at the same time the piece is rotated around its central line i.e. its longitudinal axis. At the final stage of the wrapping, the film is cut, and the end of the film is welded on the other films by means of hot sealing. As to the techniques involved in cutting, sealing and feeding of the film, reference is made e.g. to the patent publication U.S. Pat. No. 5,092,109. During the wrapping the wrapping film is stretched in a controlled manner as presented for example in the patent publication U.S. Pat. No. 5,054,263. The wrap can be guided around the mantle and the ends of the piece in such a way that the piece is rotated both around the longitudinal axis and a typically vertical axis which is transverse to the longitudinal axis. An example of such a device is disclosed in the patent publication U.S. Pat. No. 5,487,255. Alternatively, the carriage feeding the wrap can rotate around an axis vertical with respect to the piece, wherein the piece is typically only rotated around its horizontal central line.
When rolls are manipulated, for example packed in a wrap or transferred to a new working station, they have to be rotated around their longitudinal axis. Although the rolls, such as paper rolls, are nominally cylindrical, the softness of the material in the roll, the directional errors in the wrapping, variations in humidity and other factors effect the actual shape to be conical. The conical shape results in that the presently used rotating devices deflect the direction of the longitudinal axis of the roll during the rotation. This, in turn, causes errors in other work stages, such as packing effected by means of wrapping.
The problem occurs especially in devices according to the patent publication U.S. Pat. No. 5,487,255, in which conical rolls are rotated in a recess formed in a continuous track. The track is formed around two reels which are rotated, and the aim is to rotate the roll around its longitudinal axis substantially in its position by means of the moving track.
Heretofore, attempts have been made to solve said problem with separate blocking rolls and wheels. These, however, cause dents on the roll which impair the quality of the roll, and they are also expensive and cumbersome.
It is an aim of the invention to eliminate this drawback and to attain a method and a device, in which, without impairing the quality of the roll, the axle of the roll does not tend to swing during rotation even though the roll has the shape of a cone. This eliminates the errors caused by the swinging in the manipulation of the rolls.
Said problem occurs especially in soft rolls. The best solution for rotating these rolls is a slat chain trough in which the roll is rotating.
According to the invention, the act of rotating the roll so that the roll does not swing can be attained by shaping the surface of the trough in such a way that the slope angle of the profile of the surface changes in the direction of the axis of the roll. The roll is positioned in such a location during the rotation that the axle of the roll is parallel to the axis of rotation, and thus, the roll does not tend to swing.